The present invention relates to a method for uniformly sealing grooves, in a substrate having fine grooves for use in electronic devices such as semiconductor devices, with a siliceous material, and to a substrate, having a siliceous coating formed thereon, obtained by said method.
The production of electronic devices such as semiconductor devices involves such steps as the formation of insulating coatings between transistor elements and bit lines, between transistor elements and capacitors, between bit lines and capacitors, or capacitors and metal wirings, the formation of insulating coatings between metal wirings termed Inter-Metal Dielectrics (IMDs), or the sealing of isolation grooves. In such formations and sealings, siliceous materials are generally used, and methods of formation thereof include CVD methods, sol-gel methods, siloxane polymer solution-coating methods etc.
Due to increasingly higher integration of electronic devices, grooves on the substrate are becoming more fine. When such fine grooves are sealed using conventional methods, the following problems arise.
There is a problem that when fine grooves having a groove width of 0.2 xcexcm or less and a ratio (hereinafter referred to as xe2x80x9caspect ratioxe2x80x9d) of the corresponding depth to the width of 2 or more are sealed with a siliceous material, voids tend to be generated in the inside of the grooves due to conformal nature inherent in the CVD method. As a means to inhibit the generation of such voids, there is a method (the HDP-CVD method) of forming coatings by increasing the etching rate using a high-density plasma, but there are problems with the method that the upper shoulder regions of the grooves in a substrate can also be etched by the method, deforming the shape of the grooves, the coating-forming speed can be reduced, and others.
As methods of resolving such problems inherent to the CVD method, there are sol-gel methods or siloxane polymer solution-coating methods in which a sol-gel solution or a siloxane polymer solution is applied onto a substrate having fine grooves, which is then dried to seal the fine grooves, then heated to be converted into a siliceous material. However, during heating, sol-gel solutions and siloxane polymers are generally accompanied by dehydration or dealcoholization condensation, so that there occurs a considerable shrinkage in volume during the conversion into siliceous materials. Thus, there arises a problem that when fine grooves having a groove width of 0.2 xcexcm or less and an aspect ratio of 2 or more are sealed with a siliceous material, the density of the siliceous material in the inside of the fine grooves markedly decreases more than the density of the area around the surface on the outside of the grooves due to constraint on the wall surface of grooves. Thus, in the sol-gel methods or the siloxane polymer solution-coating methods, it is difficult to seal fine grooves so as to obtain a uniform density from the coating surface to the bottom of the fine grooves.
As a method that permits conversion into a siliceous material without concomitant condensation reactions, there is a method in which a polysiloxane solution is applied and dried to seal fine grooves, and then is heated. However, since polysilazanes containing organic groups such as hydrocarbon groups and alkoxy groups undergo decomposition of the organic groups, there occurs a shrinkage in volume during conversion into a siliceous material. Thus, there is a problem that when fine grooves having a groove width of 0.2 xcexcm or less and an aspect ratio of 2 or more are sealed with a siliceous material by a method that uses an organic group-containing polysilazane, the density of the siliceous material in the inside of the fine grooves markedly decreases due to a constraint on the wall surface of grooves, as in the above-mentioned sol-gel method, more than the density of the area around the surface on the outside of the grooves. Polysilazanes having an average molecular weight greater than a specific value, even when they do not contain organic groups, tend to exhibit a considerable shrinkage in volume during conversion into a siliceous material, and similar problems will arise.
Polysilazanes that do not contain organic groups and that have an average molecular weight greater than a specific value tend to exhibit reduced sealability to fine grooves during application, and tend to generate voids etc. in the inside of fine grooves as in the CVD method.
When the density of a siliceous material in the fine groove is not uniform, formation of penetrating holes in the subsequent step of through hole formation becomes difficult, and variation in the characteristics as an insulating material occurs. Such nonuniformity in density poses a problem among a plurality of fine grooves having different widths, as well as between the inside and the outside of fine grooves, because generally the finer the grooves are, the lower the density becomes, due to larger affect from the wall surface of grooves. Considering that grooves in a substrate will become even finer due to much higher integration of electronic devices in the future, there is a need for methods that can attain uniform sealing of such grooves, regardless of the inside or outside, and width, of the grooves. Thus, it is an object of the present invention to provide a method that permits uniform sealing of fine grooves with a siliceous material which was difficult in the conventional methods mentioned above.
In order to attain the above objective, the present invention intends to provide a method for sealing a fine groove with a siliceous material, characterized as comprising applying a solution of a perhydropolysilazane having a weight average molecular weight in the range of 3,000 to 20,000 in terms of polystyrene to a substrate having at least one groove having a width of 0.2 xcexcm or less at its deepest portion and having a ratio of the corresponding depth to the width of 2 or more, to thereby fill and seal the groove with the perhydropolysilazane, and then heating the perhydropolysilazane in an atmosphere containing water vapor to thereby convert the perhydropolysilazane to a siliceous material.
Furthermore, the present invention intends to provide a substrate having siliceous coating formed thereon comprising a substrate containing at least one groove having a width of 0.2 xcexcm or less at its deepest portion and having the ratio of the corresponding depth to the width of 2 or more and a siliceous coating formed thereon to fill and seal said groove, wherein said siliceous material coating is substantially free of voids in the inside of the groove, and the etching rate of said groove at its deepest portion is three times or less the etching rate on the surface of said siliceous material coating.